The present invention relates to oximeters, and in particular to analog waveform displays in pulse oximeters.
Pulse oximetry is typically used to measure various blood chemistry characteristics including, but not limited to, the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and the rate of blood pulsations corresponding to each heartbeat of a patient. Measurement of these characteristics has been accomplished by use of a non-invasive sensor which scatters light through a portion of the patient's tissue where blood perfuses the tissue, and photoelectrically senses the absorption of light in such tissue. The amount of light absorbed at various frequencies is then used to calculate the amount of blood constituent being measured.
The light scattered through the tissue is selected to be of one or more wavelengths that are absorbed by the blood in an amount representative of the amount of the blood constituent present in the blood. The amount of transmitted light scattered through the tissue will vary in accordance with the changing amount of blood constituent in the tissue and the related light absorption. For measuring blood oxygen level, such sensors have typically been provided with a light source that is adapted to generate light of at least two different wavelengths, and with photodetectors sensitive to both of those wavelengths, in accordance with known techniques for measuring blood oxygen saturation.
Known non-invasive sensors include devices that are secured to a portion of the body, such as a finger, an ear or the scalp. In animals and humans, the tissue of these body portions is perfused with blood and the tissue surface is readily accessible to the sensor.
Pulse oximeters, after processing the sensor data and calculating oxygen saturation, present that information to a display. In some pulse oximeters, it is also desirable to display the analog waveform itself. For example, U.S. Pat. No. 6,188,470 shows a signal for a display reflecting the waveform. U.S. Pat. No. 6,385,471 also discusses a waveform display, and sets forth that the data is first digitized, prefiltered, and then reconstructed for the display.
Nellcor Puritan Bennett, the assignee of the present invention, provides analog outputs in a number of its products. The analog outputs are used for such purposes as synchronizing to other instruments (e.g., EKG, multi-parameter monitor) as well as for a display, The analog waveforms are sometimes provided from the hardware pre-processing circuitry, to insure the analog signal is close in time to the actual patient waveform.
A problem with providing an analog waveform to a display after processing is that the processing takes some time, and thus the signal provided is delayed and not real-time.